Cone microphone



Oct. 30, 1956 N. MILLER 2,769,161

CONE MICROPHONE Filed Jan. 1, 1944 740 4'0 0 w f/G. 3 54 77 i l l I I ATTO NEY United States Patent CONE MICROPHONE Laymon N. Miller, Cambridge, Mass., assignor to the United States of America as represented by the Secretary of the Navy Application January 1, 1944, Serial No. 516,724

1 Claim. (Cl. 340-8) This invention relates in general to magnetostrictive transducers and in particular to an improved magnetostrictive pick-up of compressional waves for use in a sound operated mine or torpedo. This invention constitutes an improvement on the magnetostn'ctive pick-up disclosed in the C. K. Stedman et a1. Patent No. 2,626,380 and Serial No. 502,077, filed Sept. 11, 1943.

In those disclosures the casing of the mine or torpedo was used as the diaphragm of the pick-up to collect the compressional .waves. In one application the magnetostrictive tube is connected substantially directly to the casing. And in the other application, it is connected to the casing through a metal cone having its large end fitted snugly to the casing. In the second application, the cone has its base carefully fitted to the inside surface of the casing of the head of the mine, which is in the shape of a spherical shell. After grinding the base of the cone to get a close fit, it was secured by means of a thin coat of solder reinforced by an axial screw. The close fit was necessary to get good transmission for the Waves through the casing from the water into the cone. Bailies were used to localize the area of the casing used as the diaphragm, but they are ineffective for the purpose of filtering the waves received by adjacent portions of the casing. These adjacent waves are picked up by the unit and they are combined out of phase with those from the diaphragm proper, which results in an irregular response curve similar to that illustrated in Figure 3. One serious disadvantage of this irregularity is to decrease the sensitivity of the pick-up.

Another disadvantage resulting from the use of the casing as the diaphragm arises in the construction of the mine or torpedo head. The pick-up units are welded in place and the head is filled with explosive, as in a projectile; consequently, no work or adjustment can be done upon the pick-up units after completion of the heads which is a very distinct disadvantage in a device of this nature.

It is an object of this invention to so construct a compressional wave pick-up for a mine or torpedo head that Will respond faithfully to the waves impinging directly upon the diaphragm.

Another object of this invention is to eliminate from a compressional wave pick-up distorting vibrations from adjacent structure.

Another object of this invention is to improve the directional characteristics of the compressional wave pick-up.

Another object of this invention is to increase the sensitivity of a compressional wave pick-up for a mine or torpedo head.

Another object of this invention is to so construct a compressional wave pick-up for a mine or torpedo head that it may be disassembled and adjusted after the head has received the explosive charge.

Another object is to provide a compressional Wave pickup which will be economical to manufacture, reliable in operation and which possesses all of the qualities of ruggedness and dependability in service.

Other objects and features will become apparent upon a careful consideration of the following detailed description when taken together with the accompanying drawings, the figures of which are designed for the sole purpose of illustration and not as a definition of the limits of the invention, reference for the latter purpose being had to the appended claim.

In the drawings:

Figure 1 is a sectional view of part of a spherical mine or torpedo head, illustrating the improved compressional wave pick-up of this invention.

Figure 2 is an elevational view of conical diaphragm.

Figure 3 represents the response curve of an unslotted diaphragm.

Figure 4 represents the response curve of a slotted diaphragm.

Figure 5 shows a mine or torpedo, illustrating an op tional arrangement of the compressional wave pick-ups.

Fig. 6 is a cross-sectional view of the upper portion of the conical diaphragm shown in Fig. 2.

Before proceeding with a detailed description of this invention, it should be pointed out that the prior art illustrates a continuous shell or casing 11 without apertures for the pick-up units. The cone 15 was secured to the inside of casing 11. The compressional waves entered casing 11, passed across the joint of casing to cone, said joint reducing their amplitude and reflecting them somewhat; thence on through the cone to the magnetostrictive tube to operate upon the magnetic field. Obviously, once the pick-up unit was installed and the head poured with explosive, no further work or adjustment upon the pick-up was possible.

Since the directional pattern of the response of these pick-up units are equally as important as the signals themselves, the continuous casing 11 of the prior art transmits laterally to the cone signals from adjacent areas, which not only distorts the directly received signal but also the directional pattern of the response.

Applicants invention consists in the construction of a compressional wave pick-up unit, as illustrated in Figures 1 and 2, that is free of the disadvantages inherent in the devices of the prior art.

In Figure 1 the casing 11 of the mine or torpedo is pierced by a circular opening slightly larger than the circumference of the diaphragm 15. A circular ring 13, having a shoulder facing the opening, is welded to the inside of the casing as at 24. The shell of the pick-up unit 26 is fastened to this ring, with the lead wires 25 extending upwardly out of the head. Obviously, this much of the pick-up unit is all that is required to be installed until the completion of the mine or torpedo head.

The coil 21 .is mounted in the upper portion of shell 26, making the unit ready for the mounting of the movable elements. Brass cone 15 has the magnetostrictive tube 18 connected to its pointed end. The tube 18 contains a strong permanent magnet 20 which furnishes the mag netic field for inducing the signals .in coil 21. The cone 15 is fastened in place by inserting a gasket 14 between the shoulder 16 and the ring 13, and inserting bolts 22 through openings 23 in shoulder 16 and threaded into ring 13. The face of cone 15 ,is brought flush with that of the casing 11.

Figure 2 represents an enlarged view of cone 15 showing its features in greater detail. The magnetostrictive tube 18 is made integral with cone 15 by solder at 19. The base of the cone is given the same spherical contour as that of casing 11. Applicant constructed the cone 15 without the groove 17 and tested the sensitivity of the unit for angles from to +90 in respect to the axis of the cone. The results are illustrated in Figure 3, which show improvement over that of the prior art, but also indicates that the unit still has some distortion from the adjacent areas, as evidenced by the ruggedness of the curve. Applicant found that by inserting groove 17 in the shoulder 16 of cone 15, so that it is approximately'one eighth of an inch Wide and of a depth such that approximately one sixteenth of an inch of metal remains between the bottomof the groove and the face of the cone, the entire cone acted as a free piston diaphragm, essentially free of distortion, and giving the excellent response characteristics illustrated in Figure 4. These improvements are believed to result in a decided step in advance of the prior art and to merit invention of a high order. 7

In operation of the compressional waves in'the water, such as those from the propeller of a ship, impinge upon the base of cone 15, enter it, and progress toward the apex in concentrated form on the lower end of the nickel magnetostrictive tube 18. The alternating thrusts andpulls on this tube 18 against its inertial reaction generate lines of a magnetic field along the length of the tube. This is the well known inagnetostriction efiect. More precisely, there is a magnetic field in the tube 18 caused by the permanent magnet therein, and a superposed alternating field is generated in the coil at the frequency of the compressional waves. The tube 18 has a natural mechanical period for longitudinal: Waves and the frequency of such waves is the optimum frequency for operation of the pick-up. The fluctuating magnetic field linking with coil 21 generates a corresponding current therein, which is amplified andutilized in the manner disclosed in the above referred to applications for patent.

Figure 5 illustrates a modified'form of apparatus in which this invention may be used. The mine or torpedo has the pick-up units located around the periphery of the cylindrical part of the casing as shown at 81 In front of the units and behind the head a chassis 7 for tubes and the like is located; And in the rear of. the pickups the batteries 9 are placed. The positions, of the various devices illustrated representonly one of many that can be utilized. Applicant doesnotlimit himself to those positions illustrated, because many factors may make a change of position of certain elements desirable. For example, the simplicity of construction may make it d. highly desirable to locate certain elements in a specified manner, likewise the ruggedness of construction.

' Iclaim:

An apparatus operatively responsive to compressional wave energy comprising a fluid-tight casing surrounding said apparatus and having a hemispherical head portion, said head portion having an opening therethrough, a reinforcing ring securedto the inside surface of said head portion around the border of said opening, said ringhaving an inwardly projecting portion forming an integrally recessed shoulder at said opening, a. 'compartmenting shell secured to said ring, a'conical sound-transmitting body member having" an integral and homogeneous flange disposed circumferentially 'at the bas'e thereof, the base of said member and adjacent surface of said flange having a contour conforming with external surface of said hemispherical head portion at said aperture, whereby said body member whenifitt ed into said opening with the flange and recessed shoulder in abutting relation will present an unvarying surface with said head portion, circumferential- 1y disposed-meansfor securing said flange to said recessed shoulder, a peripheral groove'in said flange intermediate said securing means'and'said' base for isolating said' bod'y member from casing transmitted compressional wave energy, and means containedwithin said shell and connected to-the vertexof said-cone for faithfully converting said compressional wave energy to electrical energy. 1

References Cited' inthe .file of this-patent V UNITED. STATES PATENTS 1,4013024 Wood et al. Dec. 20; 1921 13960340 Clement May 29,1934 2,0443807 Noyes June 2 3; 1936 2,063j944 Pierce Dec. 15, 1936 2,063,950 Steinberger Dec; 15, 1936 7 2,088,324 John .a July 27, 1937 2,170,206- Mason- Aug. 22, 1939' or FOREIGN PATENTS 101,140 Sweden -l. Mar. 18, 1941 

